Tomato plants having a determinate growth habit are particularly desired by growers because the plants are shorter and have an earlier, concentrated flowering. This growth habit is generally recognized as being conferred by the presence of the sp allele (Tigchelaar, Tomato Breeding In: M. J. Bassett, ed. BREEDING VEGETABLE CROPS AVI, Westport, Conn., 1986). The determinate trait is important from an economic standpoint since concentrated flowering results in concentrated fruit set which translates to reduced harvest costs because more fruit are picked per harvest. In extreme northern and southern latitudes, full yield potential is not realized from indeterminate varieties due to the occurrence of frost. In tropical and sub-tropical areas, full yield potential is not fully realized from indeterminate varieties due to the onset of disease. In each of these situations, the use of determinate varieties increases the probability of realizing full yield potential.
Most commercial cherry tomato varieties are indeterminate (e.g., Red Cherry, Large, Cherry Sweet, Sweet 100, and Sweet Chelsea). Several determinate commercial cherry tomato varieties have been developed (e.g., Baxter's Early Bush, Cherry Grande, and Mountain Bell which are available from e.g., Tomato Growers Supply Co., Fort Meyers, Fla. and Rogers NK Seed Co., Boise, Id.). More recently new determinate cherry tomato varieties have been developed (e.g., EY 12, EY 14, EY 15, Zeraim Gedera, Gedera, Israel) but their status as commercial or garden varieties has not been established.
Another desirable trait in tomato cultivars is delayed-ripening fruit. BR 124, BR 140 (available from Hazera Seed Co., Rehovot, Israel) and FA 138 (available from Zeraim Gedera, Gedera, Israel) are known ripening-delayed cherry tomato varieties. All of these varieties are indeterminate.
In tomato, the main value of non-ripening or ripening-delayed fruit relates to fruit quality (flavor, shelf life) and durability. Since vine-ripened fruit of normal tomato varieties often cannot survive the rigors of harvesting, packing, and shipping (due to loss of firmness), the majority of tomatoes available in the market place are picked at the green stage when they are most firm, but have not yet reached peak flavor. Ripening-delay allows the tomato to reach its peak in flavor yet still retain sufficient firmness to survive harvest, packing, and shipping.
In tomato, several mutations have been reported to slow or inhibit ripening. These include dg, Nr, nor, and rin (Tigchelaar & Stevens, Plant Breeding Reviews 4:273-311 (1986)). These mutations are believed to interrupt the normal climacteric ripening pattern of tomato fruit. The best characterized of these mutations are nor and rin. In terms of inheritance and phenotype, both mutations are similar. In the homozygous state, nor and rin fruit do not fully ripen and are hence referred to as non-ripening plants. In the heterozygous state these mutations result in delayed-ripening (compared to normal ripening of wild type fruit). This intermediate phenotype means that the mutations are semi-dominant (Kopeliovitch, et al., J Amer. Soc. Hort. Sci. 107(3):361-364 (1982)). The ripening inhibition reported in the tomato line Alcobaca has been shown to be caused by a mutation in an allele of nor (Lobo, et al., J Amer. Soc. Hort. Sci. 109:741-745 (1984)). The mutation Nr results in fruit that do not ripen fully (only to a pale orange) and may be the basis for the long shelf life of the variety Longkeeper. The mutation dg has not been as well characterized as the other mutations. The mutation appears to delay fruit softening (Tong, et al., J. Amer. Soc. Hort. Sci. 114:635-638 (1989)).
Several determinate, ripening-delayed large-fruited tomato varieties are known (e.g., BR 84 (Hazera Seed Co.), Pik Ripe based on rin (Peto Seed Co., Saticoy, Calif.) and Lenor and Elenor based on nor (Pioneer Seed Co., Woodland, Calif.)). The prior art, however, lacks determinate, ripening-delayed yellow cherry tomato varieties. The present invention addresses these and other needs.
Definitions
As used herein the term "cherry tomato" is used to refer to tomato varieties which have ripe fruit weight in the range of about 10 to about 30 grams, typically between about 15 and about 25 grams. The ripe fruit have a diameter between about 1.9 to about 3.8 cm, typically between about 2.5 and 3.0 cm. The shape of cherry tomato fruit are usually globular to slightly elliptical (i.e., fruit width and fruit length are about equivalent). Cherry tomato fruit differ from small-fruited pear-type varieties in that pear fruit are fully elliptical (i.e., fruit length is greater than fruit width) and from other varieties by virtue of lower fruit weight and fruit diameter.
Cherry tomatoes are sometimes designated as Lycopersicon esculentum var. cerasiforme. It is generally accepted that cultivated tomato lines were derived from var. cerasiforme via domestication (Jenkins, Econ. Bot. 2:379-392 (1948)). The main differences between the cerasiforme type and standard tomato cultivars is that the fruit of the cerasiforme types are less than half the size of the cultivated forms (see, Rick, Econ. Bot. 12:346-367 (1958)). The cerasiforme types can also be distinguished from the cultivated types by the presence of a slightly exserted stigma in the flowers (Taylor, Biosystematics of The Tomato. In: Atherton and Rudich, eds. THE TOMATO CROP. Chapman and Hail, NY, NY, 1986). Smaller fruit size is probably the main reason that some cherry tomato varieties are designated as cerasiforme types.
The term "yellow cherry tomato" refers to a tomato that is less than half the size of the cultivated tomato, with yellow ripe flesh and clear skin.
The term "determinate habit" is used herein to refer to growth of tomato varieties which have two or fewer nodes between inflorescences. Plants having a determinate habit can be distinguished from indeterminate types, which have three or more nodes between each inflorescence (see, Tigchelaar, supra).
As used herein, the terms "delayed-ripening" or "ripening-delayed" are used to refer to tomato plants which are heterozygous for an allele which inhibits the maturation of fruit of the plant. Fruit of plants that are homozygous for the allele do not ripen and are referred to as non-ripening. As discussed above, such alleles include dg, Nr, nor, and rin. Generally, ripening-delayed tomatoes of the invention are distinguished from normal-ripening plants in that at least 50% more marketable fruit remain after 15 days of storage at 20.degree. C. in ripening-delayed plants. The precise phenotype of a plant having the ripening-delayed trait will depend upon the particular gene. A summary of phenotypes of plants having various alleles is summarized in Table 1.
TABLE 1 Tomato ripening-mutants Chromo- Phenotype of fruit homozygous Name some for the mutation Ripening 5 Fruit do not fully ripen fully and inhibitor soften very slowly. Final fruit color is yellow (rin) Fruit lack normal tomato flavor and store for a very long time. Non-ripening 10 Similar to rin but final fruit (nor) color is pale orange. Never-ripe 9 Final fruit color is orange and (Nr) soften slowly. Greenflesh 8 Ripe fruit appear red-brown in (gf) color. Chlorophyll loss is incomplete. Yellowflesh 3 Ripe fruit are yellow. (r) Lycopene is not synthesized. Fruit are otherwise normal. Alcobaca 10 Fruit ripened attached to the (alc) vine are pale red. The flavor is almost normal but storability is increased due to a slow softening rate. Fruit picked mature green show reduced ethylene production and respiration. Ripen to a yellow color. Longkeeper 10 Fruit ripen to a golden-orange-red color. Polygalacturonase activity, softening and carotenoid synthesis are much reduced. Fruit store for a long time. Tangerine 10 Fruit are a rich tangerine (t) color owing to the replacement of lycopene by prolycopene. The fruit are otherwise normal. Uniform 10 Immature fruit lack dark- ripening (u) green shoulder. (From Grierson and Kader Fruit Ripening and Quality In: Atherton and Rudich, eds. THE TOMATO CROP. Chapman and Hail, NY, NY, 1986).
As used herein a plant, seed, or fruit is "derived from" a second plant if it arises directly or indirectly from the second plant. Thus, a derived plant may be an F.sub.1 or more removed generation produced by standard breeding techniques using the second plant as parent. Alternatively, the derived plant may result from in vitro culture of tissue from the second plant using standard tissue culture and plant regeneration techniques.